Without limiting the scope of the invention, its background will be described with reference to a hydraulic chamber in an aircraft as an example.
In an aircraft hydraulic system, hydraulic fluid supply and pressure is maintained using a hydraulic reservoir. The typical reservoir design incorporates a moving piston in a chamber to accommodate changes in reservoir volume. The reservoir volume will change as a result of temperature fluctuations, system leaks and differential actuator fluid exchange. The piston position in the chamber changes proportional with the change in reservoir fluid level. By measuring the position of the piston in the chamber, the fluid level in the reservoir can be measured.
In one system, fluid level may be indicated using a graduated rod attached to the piston that extends outwardly from the chamber. It has been found, however, that the rod must be equal in length to the entire piston travel in order to provide the required fluid level readings. Due to space limitations in many aircrafts, however, using a rod to indicate fluid level in the hydraulic reservoir is impractical.
To overcome these space constraints, attempts have been made to design a fluid level indicator for the hydraulic reservoir of an aircraft that does not require additional space next to the reservoir piston. For example, in one design, an indicator tube is mounted adjacent to the hydraulic reservoir that has a floating indicator disposed therein. The floating indicator is tied directly to the piston using a pulley and cabling system. It has been found, however, that like the graduated rod level indicator, having the level indicating device attached directly to the piston may induce failures in the reservoir piston if the level indicating device becomes restricted from moving or jammed. Additionally, it has been found that the accuracy of such devices may be affected by the high vibration, high shock loads and high g-forces experienced in certain aircraft.
Therefore, a need has arisen for a fluid level indicator for indicating the level of a fluid in a chamber having a piston. A need has also arisen for such a fluid level indicator that is not physically tied to the reservoir piston. Further, a need has arisen for a such a fluid level indicator that does not require substantial space next to the chamber.